Terminal complement complexes (SC5b-9) in cerebrospinal fluid in autoimmune nervous system diseases

Immortalized Human Conjunctival Epithelial Cells Produce Functional Complement C3 and C4 Proteins

PURPOSE

The aim of this study was to assess whether complement proteins C3 and C4 are produced by immortalized human conjunctival epithelial (HCjE) cells.

METHODS

Supernatants and cell lysates from undifferentiated and differentiated HCjE cells were assayed for C3 and C4 by enzyme-linked immunosorbent assay. To measure complement protein function, supernatants and lysates were treated with heat-aggregated IgG, and soluble C5b-9 was measured.

RESULTS

C3 was upregulated in supernatants from differentiated HCjE cells compared with undifferentiated HCjE cells (556.55 ± 91.75 vs. 56.95 ± 12.09 ng/mL, P <0.001). C4 was also increased in supernatants but to a much lesser extent (0.599 ± 0.476 vs. 0.172 ± 0.0133 ng/mL, P = 0.03). From HCjE cell lysates, total C3 production was 9.03 times higher in differentiated HCjE cells ( P <0.001), whereas total C4 remained relatively unchanged. After activation with heat-aggregated IgG, sC5b-9 could be detected from both undifferentiated and differentiated HCjE cell lysates, but not in the HCjE supernatants.

CONCLUSIONS

HCjE cells produce C3 and C4 in sufficient quantities to support the formation of sC5b-9, confirming their biological activity and suggesting that HCjE cells likely produce all complement proteins C1 through C9.

Soluble membrane attack complex is diagnostic for intraventricular shunt infection in children

BACKGROUND

Children treated with cerebrospinal fluid (CSF) shunts to manage hydrocephalus frequently develop shunt failure and/or infections, conditions that present with overlapping symptoms. The potential life-threatening nature of shunt infections requires rapid diagnosis; however, traditional microbiology is time consuming, expensive, and potentially unreliable. We set out to identify a biomarker that would identify shunt infection.

METHODS

CSF was assayed for the soluble membrane attack complex (sMAC) by ELISA in patients with suspected shunt failure or infection. CSF was obtained at the time of initial surgical intervention. Statistical analysis was performed to assess the diagnostic potential of sMAC in pyogenic-infected versus noninfected patients.

RESULTS

Children with pyogenic shunt infection had significantly increased sMAC levels compared with noninfected patients (3,211 ± 1,111 ng/ml vs. 26 ± 3.8 ng/ml, P = 0.0001). In infected patients undergoing serial CSF draws, sMAC levels were prognostic for both positive and negative clinical outcomes. Children with delayed, broth-only growth of commensal organisms (P. acnes, S. epidermidis, etc.) had the lowest sMAC levels (7.96 ± 1.7 ng/ml), suggesting contamination rather than shunt infection.

CONCLUSION

Elevated CSF sMAC levels are both sensitive and specific for diagnosing pyogenic shunt infection and may serve as a useful prognostic biomarker during recovery from infection.

FUNDING

This work was supported in part by the Impact Fund of Children's of Alabama.

Increased soluble C5b-9 in CSF of neuromyelitis optica

Neuromyelitis optica (NMO) and multiple sclerosis (MS) are two of the autoimmune inflammatory demyelinating diseases in the central nervous system. Complement is thought to have an important role in pathogenesis of these diseases, especially in NMO. However, the change of terminal complement complex (TCC, C5b-9) in patients with NMO is still unclear. Cerebrospinal fluid (CSF) C3a, C5a, sC5b-9 were measured by enzyme-linked immunosorbent assay in patients with NMO (n = 26), MS (n = 25) and other neurological disease (OND, n = 19). CSF levels of C5a in patients with NMO were higher than patients with OND (P = 0.006). Increased CSF sC5b-9 were found in the patients with NMO compared with patients with MS (P = 0.029) and OND (P = 0.0001). CSF sC5b-9 in patients with MS were also higher than patients with OND (P = 0.030). Patients with NMO revealed a trend to an increased disease disability with increased CSF sC5b-9 during relapse but not in MS (NMO: P = 0.006, MS: P = 0.097). CSF levels of sC5b-9 are increased in patients with NMO and reflect the activation of complement in NMO.

IgG glycan hydrolysis by EndoS inhibits experimental autoimmune encephalomyelitis

Studies in experimental autoimmune encephalomyelitis (EAE), a mouse model of multiple sclerosis, have shown that B cells markedly influence the course of the disease, although whether their effects are protective or pathological is a matter of debate. EndoS hydrolysis of the IgG glycan has profound effects on IgG effector functions, such as complement activation and Fc receptor binding, suggesting that the enzyme could be used as an immunomodulatory therapeutic agent against IgG-mediated diseases. We demonstrate here that EndoS has a protective effect in myelin oligodendrocyte glycoprotein peptide amino acid 35–55 (MOG_35-55)-induced EAE, a chronic neuroinflammatory demyelinating disorder of the central nervous system (CNS) in which humoral immune responses are thought to play only a minor role. EndoS treatment in chronic MOG_35-55-EAE did not impair encephalitogenic T cell priming and recruitment into the CNS of mice, consistent with a primary role of EndoS in controlling IgG effector functions. In contrast, reduced EAE severity coincided with poor serum complement activation and deposition within the spinal cord, suggesting that EndoS treatment impairs B cell effector function. These results identify EndoS as a potential therapeutic agent against antibody-mediated CNS autoimmune disorders.

Membrane attack by complement: the assembly and biology of terminal complement complexes

Complement system activation plays an important role in both innate and acquired immunity. Activation of the complement and the subsequent formation of C5b-9 channels (the membrane attack complex) on the cell membranes lead to cell death. However, when the number of channels assembled on the surface of nucleated cells is limited, sublytic C5b-9 can induce cell cycle progression by activating signal transduction pathways and transcription factors and inhibiting apoptosis. This induction by C5b-9 is dependent upon the activation of the phosphatidylinositol 3-kinase/Akt/FOXO1 and ERK1 pathways in a Gi protein-dependent manner. C5b-9 induces sequential activation of CDK4 and CDK2, enabling the G1/S-phase transition and cellular proliferation. In addition, it induces RGC-32, a novel gene that plays a role in cell cycle activation by interacting with Akt and the cyclin B1-CDC2 complex. C5b-9 also inhibits apoptosis by inducing the phosphorylation of Bad and blocking the activation of FLIP, caspase-8, and Bid cleavage. Thus, sublytic C5b-9 plays an important role in cell activation, proliferation, and differentiation, thereby contributing to the maintenance of cell and tissue homeostasis.

Neuroprotective effects of the complement terminal pathway during demyelination: implications for oligodendrocyte survival

Multiple sclerosis (MS) is a chronic inflammatory demyelinating disease of the central nervous system that is mediated by activated lymphocytes, macrophages/microglia, and complement. In MS, the myelin-forming oligodendrocytes (OLGs) are the targets of the immune attack. Experimental evidence indicates that C5b-9 plays a role in demyelination during the acute phase of experimental allergic encephalomyelitis (EAE). Terminal complement C5b-9 complexes are capable of protecting OLGs from apoptosis. During chronic EAE complement C5 promotes axonal preservation, remyelination and provides protection from gliosis. These findings indicate that the activation of complement and C5b-9 assembly can also have protective roles during demyelination.

B-cells and humoral immunity in multiple sclerosis. Implications for therapy

B-cells and humoral immunity have been implicated in the pathogenesis of multiple sclerosis. The most common pattern of demyelinating pathology in multiple sclerosis is associated with the deposition of antibodies and the activation of complement, as well as T-cells and macrophages. Plasmapheresis has been found to be an efficient therapeutic approach in patients with this type of pathological lesion. Recent data have indicated that autoantibodies and complement C5b-9 may be involved in lesion formation and might also be beneficial for lesion repair. Thus, the role played by B-cells and humoral immunity is rather complex, and new strategies for targeting B-cell responses are continuing to emerge.

Complement activation in autoimmune demyelination: Dual role in neuroinflammation and neuroprotection

Multiple sclerosis and its animal model experimental allergic encephalomyelitis are inflammatory demyelinating diseases of the central nervous system mediated by activated lymphocytes, macrophages/microglia and the complement system. Complement activation and the C5b-9 terminal complex contribute to the pathogenesis of these diseases through its role to promote demyelination. C5b-9 was also shown to protect oligodendrocytes from apoptosis both in vitro and in vivo. Our findings indicate that activation of complement and C5b-9 assembly plays a pro-inflammatory role in the acute phase, but may also be neuroprotective.

The complement system in central nervous system diseases

The activation of complement system is important factor in inflammatory, neurodegenerative and cerebrovascular diseases. CNS cells are able to synthesize complement components, and myelin and oligodendrocytes (OLG) are known to activate the classical pathway of complement in vitro in the absence of antibodies. Although activation of the complement system is known to promote tissue injury, recent evidence has also indicated that this process can have neuroprotective effects. In particular, terminal C5b-9 complexes enhance OLG survival both in vitro and in vivo. Complement activation may also reduce the accumulation of amyloid and degenerating neurons by promoting their clearance and suggest that certain inflammatory defense mechanisms in the brain may be beneficial in neurodegenerative disease. Complement system activation plays also an important role in brain damage after ischemic injury or head trauma. These findings strongly suggest that complement activation and membrane assembly of C5b-9 can play a role in injury but can also provide neuroprotection depending on the pathophysiological context.

C5b-9 complement complex in autoimmune demyelination and multiple sclerosis: dual role in neuroinflammation and neuroprotection

Complement system activation plays an important role in innate and acquired immunity. Activation of complement leads to the formation of C5b-9 terminal complex. While C5b-9 can promote cell lysis, sublytic assembly of C5b-9 on plasma membranes induces cell cycle activation and survival. Multiple sclerosis (MS) and its animal model experimental allergic encephalomyelitis (EAE) are inflammatory demyelinating diseases of the central nervous system (CNS) mediated by activated lymphocytes, macrophages/microglia and the complement system. Complement activation may contribute to the pathogenesis of these diseases through its dual role: the ability of activated terminal complex C5b-9 to promote demyelination and the capacity of sublytic C5b-9 to protect oligodendrocytes (OLG) from apoptosis. By inducing EAE in C5-deficient mice, we showed that complement C5 promotes remyelination and protects oligodendrocytes from apoptotic cell death. These findings indicate that activation of complement C5b-9 plays a pro-inflammatory role in the acute phase of the disease, but may also be neuroprotective during the chronic phase of the disease.

Complement C5 in experimental autoimmune encephalomyelitis (EAE) facilitates remyelination and prevents gliosis

Activation of the classical complement system is known to play a central role in autoimmune demyelination. We have analyzed the role of complement component C5 in experimental autoimmune encephalomyelitis (EAE) using C5-deficient (C5-d) and C5-sufficient (C5-s) mice. Both groups of mice displayed early onset EAE, a short recovery phase, and similar stable chronic courses. However, in contrast to the clinical similarities, marked differences were apparent by histopathology. During acute EAE in C5-d, a delay in inflammatory cell infiltration and tissue damage was observed along with restricted lesion areas, which in C5-s mice were more extensive and diffuse. More striking were the differences in chronic lesions. In C5-d mice, inflammatory demyelination and Wallerian degeneration were followed by axonal depletion and severe gliosis, while in C5-s, the same initial signs were followed by axonal sparing and extensive remyelination. In C5-d, immunohistochemistry and Western blotting showed an increase in glial fibrillary acidic protein and a decrease in neurofilament protein, proteolipid protein, and several pro-inflammatory markers. These results in the EAE model indicate that absence of C5 resulted in fiber loss and extensive scarring, whereas presence of C5-favored axonal survival and more efficient remyelination.

Membrane signaling by complement C5b-9, the membrane attack complex

The terminal complement complexes C5b-7, C5b-8 and C5b-9 are able to generate nonlethal cell signals. One universal consequence of a cell being targeted by C5b-8 or C5b-9 is an influx of Ca2+. In addition, other second messengers, including cAMP, inositol phosphate intermediates and arachidonate metabolites, are generated by the terminal complement complexes in specific cell types. In vivo, terminal complement complexes have been found in a wide variety of inflammatory processes in humans and in experimental animal models. Some of these models of inflammation putatively induced by terminal complement complexes have been tested in complement-deficient animals, and indeed no inflammation results, which supports the critical role of the terminal complement complexes in the pathogenesis of the lesion.